Trying to fix an old pc.

[menokev]

I have a 3 year old desktop that I want to fix and hopefully let my little cousin use, it is a amd athlon fx-55 with ASUS A8V mobo, 2x 512mb corsair twinx ram and a x800xt videocard. I have not touched the machine for a long time and the last time I did, I noticed that the cpu fan was no longer running and never got around to replacing it. So I recently replaced the cpu fan and to my surprise the pc shuts off after 15-20 seconds or so after turning it on, never even displays the windows xp logo and just turns itself off. Everything seems to be in working order, so what could be the problem? and how would I go about checking for the problem that is causing this? Sorry for the lack of knowledge on my part

also the power supply is 400watts

 

[jfenwick]

I've had this happen with damaged CPUs...you have another you can swap in and try?

You checked that the new cooler is on properly eh?